The hindered amines, such as the derivatives of 2,2,6,6-tetramethylpiperidine, have long been known as very effective stabilizers against the deleterious effects of actinic light. Indeed, a number of such compounds enjoy considerable economic success as light stabilizers for a host of organic substrates.
J. B. Adeniyi et al., J. Appl. Poly. Sci., 34, 2673 (1987) describes nitrones as process stabilizers for poly(vinyl chloride), PVC, in the presence of tin maleate and a hydrogen chloride scavenger. Nitrones operate by trapping radicals that are formed by mechanoscission of polymer chain.
L. P. Nethsinghe et al, Rubber Chem. Tech. 57, 779 (1984) show that N-lower alkyl-alpha-phenyl or substituted phenyl nitrones are effective antifatigue, antioxidant and antiozonant agents for vulcanized rubber.
K. B. Chakraborty et al, J. Appl. Poly. Sci., 30, 3267 (1985) disclose aldonitrones containing a phenolic group which are effective as melt stabilizers for polypropylene. These nitrones are the N-phenyl or N-tert-butyl-alpha phenyl or substituted phenyl nitrones.
A. Y. Gerchikov et al, Zh. Prikl. Khim., 1986, 1082 (C.A., 106, 4388n (1987)) describe amide substituted nitrones as antioxidants for industrial esters derived from pentaerythritol.
Japanese Sho No. 59-11345 describes the melt stabilization of olefin polymers using selected aldonitrones and ketonitrones. N-tert-butyl-alpha-phenyl nitrone is exemplified as a process stabilizer for polypropylene. Substitution on the N-atom of the nitrone is described as alkyl of 1 to 18 carbon atoms, phenyl or tolyl. Substitution on the alpha-carbon is hydrogen, phenyl or substituted phenyl.
M. Schulz et al, Plaste Kautsch. 1986, 209 (C.A. 105, 173628a (1986)) discloses the antioxidant activity of N-phenyl aldonitrones or ketonitrones as as antioxidants for polypropylene. N-tert-butyl or N-phenyl-alpha-phenyl or substituted phenyl nitrones are described.
Long chain N-alkyl-alpha-alkyl nitrones useful as process stabilizers for polyolefins are described in copending patent application Ser. No. 330,986, now U.S. Pat. No. 4,898,901.
None of these references disclose the instant compounds having both a hindered amine and a nitrone moiety in the same molecule.
The presence of the nitrone group in the instant compounds allows for the potential coupling of the instant stabilizer compounds to the polymer being stabilized by a covalent bond during the polymer processing step. The instant compounds have both a hindered amine moiety and a nitrone moiety. Such compounds are novel and allow for much greater flexibility in molecular structures than do the nitrones and hindered amines of the prior art.
This can be especially seen where the N-atom of the hindered amine is substituted by a hydrocarboxy group. Such groups are non-interacting and allow the hindered amine to be used in poly(vinyl chloride), PVC, and acid catalyzed thermoset acrylic coatings where hindered amines with high basicity sometimes cause problems